Nylon comfort fiber containing poly(N,N-dimethylacrylamide)

ABSTRACT

This invention is a nylon fiber useful for improved comfort for wearers of apparel fabric made therefrom comprising (a) from about 5 to 15 percent by weight of poly (N,N-dimethylacrylamide) having a molecular weight which in a 25% aqueous solution gives a viscosity of from about 20 to 1 000 centipoise (0.02 to 1.0 Pa.s) at 25° C. and (b) correspondingly from about 85 to 95% by weight nylon.

BACKGROUND OF THE INVENTION

This invention relates to an apparel fiber of nylon containing 5 to 15% by weight poly(N,N-dimethylacrylamide) useful for improved comfort for wearers of apparel fabric made therefrom.

Consumers have long perceived cotton as one of the most comfortable apparel fibers, and have credited this perception largely to its moisture regain. Since the invention of nylon, researchers have sought techniques which confer to nylon an equivalent sense of comfort, and have centered this effort on increasing its moisture regain. In Japanese Publication No. 73-13 337 an N,N-dimethylacrylamide-methyl acrylate copolymer was added to polyamide spinning compositions to increase the hygroscopicity of the filaments. Also, a methyl acrylate-N,N-dimethylacrylamide copolymer was used for the same purpose in Japanese Publication No. 72-42 134. It is also known in Japanese Publication No. 72-41 744 to use poly(N,N-dimethylacrylamide) to increase the melt viscosity of polyamide. In Japanese Publication No. 77-25 895, N,N-dimethylacrylamide was grafted onto a polyester or similar polymer by radiation in the presence of a catalyst and in Japanese Publication No. 71-16893-R the graft copolymer of polyamide was an acrylamide and was taught to improve hygroscopic properties. U.S. Pat. No. 4,135,877 teaches the grafting onto a polyamide fiber of N,N'-methylene-bis-acrylamide in the presence of an acid to improve hygroscopic properties. A similar teaching was found in U.S. Pat. No. 4,238,193 and a general teaching along the same lines is found in G.B. No. 1 355 846. Acrylamides are grafted onto a hollow fiber in Japanese Publication No. 55057-071.

Poly(N,N-dimethylacrylamide), hereinafter PDMAA, is prepared from a commercially available monomer and polymerizes readily using free radical initiators. The polymer is also available commercially.

SUMMARY OF THE INVENTION

This invention is a nylon fiber, useful for improved comfort for wearers of apparel fabric made therefrom, comprising (a) from about 5 to 15% of poly(N,N-dimethylacrylamide) having a molecular weight which in a 25% aqueous solution gives a viscosity of from about 20 to 1,000 centipoise (0.02 to 1.0 Pa.s) at 25° C. and (b) correspondingly from about 85 to 95% by weight nylon. The invention is also the method of preparing a nylon fiber useful for improved comfort for wearers of apparel fabric made therefrom comprising adding from about 5 to 15% by weight of poly(N,N-dimethylacrylamide) having a molecular weight which in a 25% aqueous solution gives a viscosity of from about 20 to 1000 centipoise (0.02 to 1.0 Pa.s) at 25° C. to from about 85% to 95% by weight of caprolactam, then polymerizing the mixture conventionally, then extruding and washing the resultant polymer conventionally, then forming the resultant polymer into fiber by conventional spinning. Preferably, during the method, a grafting reaction occurs during polymerization. It is also preferable to use at least 10% poly(N,N-dimethylacrylamide) added to the caprolactam. It is preferable to form the resultant polymer into fiber by spinning through a spinnerette hole having a length to diameter ratio of from about 4:1 to 8:1.

Nylon polymers were actually made containing up to 10% of PDMAA. Nylon fiber containing 10% PDMAA could be spun only when the molecular weight of the PDMAA was such that a 25% aqueous solution gave a viscosity of between 20 and 1000 centipoise. When the PDMAA molecular weight was high, only nylons containing low concentrations could be spun into yarn. At 65% relative humidity and 68° F. (20° C.) and at 95% relative humidity and 90° F. (32° C.), nylon fibers containing 10% PDMAA had a moisture regain similar to that of cotton. No antioxidants were necessary for satisfactory retention of mechanical properties in hot-wet processing of the nylon fiber and the PDMAA did not affect the light stability or dyed wash fastness in draw twist yarn.

DESCRIPTION OF THE INVENTION

During the research carried out to make this invention, various polymers listed in Table I were evaluated. Because of the concern that low molecular weight polymers may leach out during polymer washing and drying and fiber laundering, copolymers containing PDMAA and small quantities of acrylic acid were also prepared for evaluation. This polymeric system was expected to react with the nylon amine end group forming a stable branched copolymer. These copolymers did not, however, produce processable nylon due to excessive crosslinking reactions (see Table III). It turned out that this modification is unnecessary due to a slow amine-amide interchange reaction that occurred with the PDMAA homopolymer during caprolactam polymerization. This reaction was sufficient to form a stable branched copolymer, which was not affected by the washing process.

Technical data from polymers containing PDMAA are listed in Tables II and III. These tables show that polymers prepared with the lower molecular weight PDMAA samples tended to have fewer amines and fewer carboxyls, particularly at longer polymerization residence times.

The decrease in amines can be explained by a relatively slow amine-amide interchange reaction. The mechanism is probably as follows: ##STR1##

To confirm this mechanism, the effluent sweep gas was collected from a nylon polymerization containing 10% PDMAA. The analysis by gas chromatograph and mass spectrometer found 3.8 grams of dimethylamine, equivalent to 7.5% of the dimethyl amine present in the PDMAA polymer. Details of this experiment are given in Example I. This indicated that a grafting reaction occurred during polymerization. The decrease observed in carboxyls may result from the decarboxylation of any polyacrylic acid formed in the grafting reaction. Polyacrylic acid is known to decarboxylate at about 250° C.

The melt viscosity of polymers containing PDMAA is much lower than nylon homopolymers of the same formic acid viscosity (measured conventionally). This is shown in Table IV. This is consistent with the grafting reaction shown above, since graft polymers have lower melt viscosity, in which the branching segments are tightly coiled, and higher solution viscosities in which the branching segments are extended or loosely coiled than ungrafted polymers. The presence of PDMAA did not significantly lower the melting point of the nylon, nor did it significantly slow the rate of crystallization on cooling. These data are given in Table V.

Initial evaluations showed that at least 10% PDMAA in nylon was required to achieve the 13% to 14% moisture regain attributed to cotton. At this level, attempts to spin polymers containing 10% high molecular weight PDMAA resulted in filaments breaking off at the spinnerette face. In no instances, however, were there high spin pack pressures. This was true even with nylon having formic acid viscosity (FAV) of 90. When the molecular weight of the PDMAA was decreased, and the spinnerette hole length/diameter ratio increased to between 4 and 8:1, spinning performance was good. Summaries of the spinning trials and the yarn physical properties are shown in Table VI.

The moisture regains of the yarns were tested after they were scoured to remove spin finish. The data given in Table VII, show that at room temperature and 65% relative humidity, the regain of yarn with the 10% PDMAA is similar to that of scoured cotton. No change in the moisture regain was seen when the yarns were given twenty-five scouring washes.

Nylon yarns containing PDMAA were submerged in boiling water for thirty minutes, then oven dried at 150° C. The percent loss in strength was less than the control as shown in Table VIII. An antioxidant to stabilize the polymer is unnecessary. PDMAA did not affect the retention of breaking strength or of elongation after being exposed to twenty hours of carbon arc as shown in Table IX. PDMAA did not affect dyed washfastness of draw twist yarns as shown in Table X.

EXAMPLE 1

    ______________________________________                                         Caprolactam     1088    grams                                                  Aminocaproic Acid                                                                              52      grams                                                  MnCl.sub.2.4 H.sub.2 O                                                                         0.0674  gram                                                   H.sub.3 PO.sub.2 m 50% Solution                                                                0.1675  gram                                                   PDMAA, Sample No. 11                                                                           455     grams    (113.75 g solids)                             (25% Solids)                                                                   ______________________________________                                    

The starting materials were mixed together at 90° C. and poured into a 3-liter glass reactor equipped with a heating mantle and an agitator. The melt was swept with nitrogen gas and stirred and heated to 255° C. over a one-hour period at atmospheric pressure. The melt was held at 255° C. for 31/4 hours with the nitrogen sweep.

The nitrogen gas was passed through a large flask, where much of the water vapor present in the sweep gas condensed, and then two bubblers in series which originally contained solutions of 10 cc of concentrated HCl, and 40 cc of distilled water.

After polymerization was completed the contents of condensate flask and the two bubblers were analyzed for dimethylamine by use of the gas chromatograph. A total of 3.85 grams of dimethyl amine was found; 2.8 grams in the condensate flask, 1.0 gram in the first bubbler, and 0.05 gram in the final bubbler.

The nylon polymer was extruded, washed, dried and submitted for analysis. It had a 67 FAV with 42 carboxyls and 23 amines.

    ______________________________________                                         Dimethyl Amine Found, Grams                                                                           3.85                                                    Dimethyl Amine Added as PDMAA:                                                 Molecular Wt. (CH.sub.3).sub.2 NH                                                                     45.1                                                     ##STR2##              99.1                                                     ##STR3##                                                                       ##STR4##                                                                      ______________________________________                                    

The loss of 3.85 grams of dimethyl amine in 1133 grams of washed and dried polymer is 75 equivalents of amine per 10⁶ grams of polymer. Since the difference of ends in the nylon polymer is not 75, but only 19, there must have been some simultaneous loss of carboxyls. Since polyacrylic acid, a possible decomposition product, is known to lose carboxyl groups at 250°-260° C., this could explain the decrease in carboxyls.

The polymer was then extruded into water cut into pellets and washed and dried conventionally to remove water extractables such as lactam monomers, oligomers and the like.

The pellets were melted in a conventional melter and the molten polymer was pumped through a conventional spinnerette, and conventionally quenched to form fiber.

Note that a thorough discussion of N,N-(dimethylacrylamide) and its uses are found in a paper by that name, Chemical Abstracts, Vol. 83, December, 1975. This paper includes a thorough discussion on polymerization. However, the following example provides the method to polymerize dimethylacrylamide.

EXAMPLE 2

Dimethylacrylamide Polymerization

Materials Required:

N,N-dimethylacrylamide

Isopropyl Alcohol

Potassium Persulfate

Sodium Bisulfite

Boil 580 ml of deionized water while bubbling nitrogen through the water. Then allow the boiled water to cool while passing nitrogen through the water.

Dissolve 3 grams of potassium persulfate (K₂ S₂ O₈) in 50 ml of the boiled water. Dissolve 1.5 grams of sodium bisulfite (Na₂ HSO₃) and another 50 ml of the boiled water.

Pour 160 grams of dimethylacrylamide into the 480 ml of boiled water which remains. Add 20 ml of isopropyl alcohol and cool in an ice bath to 0° C.

Add 10 ml of the potassium persulfate solution and stir. Add 10 ml of the sodium bisulfite solution and stir. Bubble nitrogen through the solution for one-half hour and then allow the solution to warm to room temperature. Then heat the solution to 50° C. for one-half hour. Allow the solution to cool, and store the solution in a dark brown bottle.

                  TABLE I                                                          ______________________________________                                         PDMAA                                                                          Sample % Acrylic % Conc., Viscosity,                                                                             Pascal                                       Number Acid      Aqueous  Centipoises                                                                            Seconds (Pa · s)                    ______________________________________                                         1      0         100      --      --                                           2      0         25.4     20 000  20.000                                       3      0         25.4     354     0.354                                        4      0         25.6     4 000   4.000                                        5      0         25.0     10 000  10.000                                       6      2.0       24.5     175     0.175                                        7      5.0       24.6     200     0.200                                        8      0         25.0     25      0.025                                        9      2.0       25.0     21      0.021                                        10     0         25.5     74      0.074                                        11     0         25.0     156     0.156                                        12     2.5       25.1     79      0.079                                        13     2.5       25.5     153     0.153                                        14     5.0       25.7     76      0.076                                        15     5.0       25.2     152     0.152                                        16     0         25.6     76      0.076                                        17     0         25.0     302     0.302                                        ______________________________________                                    

                                      TABLE II                                     __________________________________________________________________________     POLYMERIZATION CONDITIONS AND PROPERTIES                                       OF PDMMA MODIFIED NYLONS                                                                 Conc.                                                                Nylon                                                                               PDMAA                                                                               in  Hours                                                            Polymer                                                                             Sample                                                                              Nylon,                                                                             at   Extrusion                                                   Number                                                                              Number                                                                              %   255° C.                                                                      Ribbon                                                                              *FAV **COOH                                                                              **NH.sub.2                                   __________________________________________________________________________     1    1    10  1    None 87   76   62                                           2    1    4   2    Fair 96   62   60                                           3    1    1   2.6  Good 51   62   58                                           4    5    5   1.8  Fair 93   68   62                                           5    5    1   2.5  Good 71   53   50                                           6    4    10  1.5  Good 102  56   47                                           7    4    5   2.2  Good 90   59   58                                           8    4    1   2.5  Good 81   52   44                                           9    3    7.3 2.5  Good 54   56   42                                           10   3    5   3.3  Good 89   53   48                                           11   3    1   3.0  Good 65   56   51                                           12   8    6   7.5  Good 53   16   13                                           13   8    5   7    Good 64   24   15                                           14   10   10  5.2  Good 57   24   12                                           15   11   10  5.7  Good 74   23   15                                           16   16   10  3.5  Good 46   40   23                                           17   17   10  2.2  Good 96   40   28                                           18   10   10  6    Good 54   20   11                                           19   10   10  5    Good 55   63   18                                           20   10   10  4    Good 53   35   22                                           21   10   5   3    Good 72   41   33                                           __________________________________________________________________________      *FAV is relative formic acid viscosity obtained by measuring the viscosit      at 25° C. of a 11% solution of the polymer in formic acid (ASTM         78962T).                                                                       **COOH indicates carboxyl groups per 10.sup.6 g polymer and NH.sub.2           indicates amine groups per 10.sup.6 g polymer measured as in U.S. Pat. No      4 356 280, Col. 4, lines 55 through 68, and column 5, lines 1 through 46,      hereby incorporated by reference.                                        

                                      TABLE III                                    __________________________________________________________________________     POLYMERIZATION CONDITIONS AND PROPERTIES                                       OF PDMAA/ACRYLIC ACID COPOLYMERS                                                         Conc.                                                                Nylon                                                                               PDMAA                                                                               in  Hours                                                            Polymer                                                                             Sample                                                                              Nylon,                                                                             at   Extrusion                                                   Number                                                                              Number                                                                              %   255° C.                                                                      Ribbon                                                                              *FAV **COOH                                                                              **NH.sub.2                                   __________________________________________________________________________     C-1  6    5   6    Good 109  52   10                                           C-2  6    1   2.5  Good 86   53   43                                           C-3  7    5   5.2  Fair 73   78   14                                           C-4  7    1   2.2  Good 83   61   44                                           C-5  9    7.5 6.5  None 20   33   18                                           C-6  9    5   6    Good***                                                                             48   43   17                                           C-7  12   10  9    None 24   52   21                                           C-8  12   5   6    Fair***                                                                             36   13   11                                           C-9  13   10  9    None 30   56   14                                            C-10                                                                               13   10  6    None 22   65   20                                           __________________________________________________________________________      *FAV is relative formic acid viscosity obtained by measuring the viscosit      at 25° C. of a 11% solution of polymer in formic acid (ASTM             78962T).                                                                       **COOH indicates carboxyl groups per 10.sup.6 g polymer and NH.sub.2           indicates amine groups per 10.sup.6 g polymer measured as in U.S. Pat. No      4 356 280, supra.                                                               ***These were the only batches containing a copolymer which could be spu      into yarn.                                                               

                  TABLE IV                                                         ______________________________________                                         MELT VISCOSITY OF NYLON POLYMERS CONTAINING                                    PDMAA (500° F. (260° C.), 33:1 Orifice at 2 000                  Seconds.sup.-1)                                                                Nylon  PDMAA    Conc.                                                          Polymer                                                                               Sample   in Nylon,        Viscosity,                                    Number Number   %          FAV   Pascal · seconds                     ______________________________________                                         Control*                                                                              --       --         53    120.0                                         C-3     7       5          73    35.0                                          14     10       10         57    49.0                                          15     11       10         74    50.5                                          9       3       7.3        54    80.0                                          ______________________________________                                          The viscosity was measured on a Monsanto Automatic Capillary Rheometer         Model 3501.                                                                    *The control polymer was an acetic acid terminated polymer containing          0.06% TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized         with 8 ppm of manganese and 10 ppm of phosphorus.                        

                  TABLE V                                                          ______________________________________                                         DSC ANALYSIS OF NYLON CONTAINING PDMAA                                         Poly-                                                                          mer   Conc. of                                                                 Num-  PDMAA                                                                    ber   Sample Number                                                                              Tm, °C.                                                                          Tg, °C.                                                                       Tch, °C.                                                                       Tcc, °C.                        ______________________________________                                         NO*   0           223      36    65     176                                    Con-  0**         225      40    66     174                                    trol                                                                           14    10% of No. 10                                                                              222      41    69     172                                    15    10% of No. 11                                                                              222      41    69     173                                    21     5% of No. 10                                                                              224      39    69     175                                    ______________________________________                                          *NO is polymer without additive or stabilizers of about 55 FAV, 55             carboxyls and 55 amines.                                                       **The control polymer is an acetic acid terminated polymer containing          0.06% TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized         with 8 ppm of manganese and 10 ppm of phosphorus.                              The DSC (Differential Scanning Calorimeter) analysis was performed on a        duPont Model 1090 Thermal Analyzer. The solid polymer was heated in            nitrogen at the rate of 10° C. per minute. The temperature at the       peak of the endotherm was taken as the melting point, Tm. The temperature      was raised to 255° C. and held for five minutes. It was then            quenched in liquid nitrogen to produce an amorphous solid. The polymer wa      then heated at 10° C. per minute. The temperature at which the hea      flow increased, before becoming steady again, was taken as the glass           transition temperature, Tg. The heating was continued at 10° C.         minute. The temperature at the peak of the exotherm was taken as the           temperature of crystallization on heating, Tch. The heating was continued      to 255° C. and then cooled at 10° C. per minute. The             temperature at the peak of the exotherm was taken as the temperature of        crystallization on cooling, Tcc.                                         

                                      TABLE VI                                     __________________________________________________________________________     SPINNING CONDITIONS AND YARN PHYSICAL PROPERTIES                               Nylon                                                                               Conc. &                                                                             Spin                                                                               Pot                UTS                                                                               %                                          Polymer                                                                             PDMAA                                                                               Temp.,                                                                             Pressure,  %   **UTS                                                                              mN/                                                                               Shrink-                                    Number                                                                              Sample                                                                              °C.                                                                         psig                                                                              kPa FAV*                                                                               UE**                                                                               gpd dtex                                                                              age                                        __________________________________________________________________________     Control   275 2200                                                                              15 200                                                                             45  61  5.4 48 17                                         10    6% of                                                                              275 2000                                                                              13 800                                                                             53  59  4.4 39 21                                              No. 8                                                                     Control   268 750                                                                               5200                                                                               40  55  4.4 39 18                                         C6    5% of                                                                              263 600                                                                               4100                                                                               48  48  3.6 32 20                                              No. 9                                                                     13    5% of                                                                              273 1050                                                                              7200                                                                               64  57  4.1 36 22                                              No. 8                                                                     Control   276 500                                                                               3400                                                                               45  65  4.5 40 17                                         14   10% of                                                                              275 400                                                                               2800                                                                               57  38  2.8 25 25                                              No. 10                                                                    15   10% of                                                                              276 500                                                                               3400                                                                               74  53  3.1 27 25                                              No. 11                                                                    21    5% of                                                                              276 1150                                                                              7900                                                                               72  60  4.1 36 21                                              No. 10                                                                    Control   270 700                                                                               4800                                                                               45  54  4.6 41 16                                         18   10% of                                                                              274 500                                                                               3400                                                                               54  56  3.1 27 21                                              No. 10                                                                    19   10% of                                                                              271 500                                                                               3400                                                                               55  49  2.9 26 21                                              No. 10                                                                    20   10% of                                                                              270 500                                                                               3400                                                                               53  52  3.1 27 20                                              No. 10                                                                    Control   264 1300                                                                              9000                                                                               45  54  4.7 41 --                                         C8    5% of                                                                              265 1800                                                                              12 400                                                                             36  20  2.8 25 --                                              No. 12                                                                    16   10% of                                                                              265 1400                                                                              9700                                                                               46  37  3.0 26 --                                              No. 16                                                                    __________________________________________________________________________      All cross sections were round; draw ratios 3.0; and deniers 110/30.            *FAV is relative formic acid viscosity obtained by measuring the viscosit      at 25° C. of a 11% solution of polymer in formic acid (ASTM             78962T).                                                                       **UE is ultimate elongation, %.                                                UTS is ultimate tensile strength in grams per denier and                       millinewtons/decitex.                                                    

                  TABLE VII                                                        ______________________________________                                         YARN MOISTURE REGAIN                                                                             Moisture Regain, %                                                     Concentration 65% RH   95% RH                                        Polymer   and PDMAA     at 68° F.                                                                        at 90° F.                              Number    Sample Number (18° C.)                                                                         (32° C.)                               ______________________________________                                         Control*                4-5      7-8                                           12         6% of No. 8  5-6       9-10                                         Control*                4-5      7-8                                           14        10% of No. 10 6-7      13-14                                         15        10% of No. 11 6-7      13-14                                         21         5% of No. 10 5-6      10-11                                         Control*                4-5      7-8                                           18        10% of No. 10 6-7      13-14                                         19        10% of No. 10 6-7      13-14                                         20        10% of No. 10 6-7      13-14                                         ______________________________________                                          All yarns were scoured once, AATCC 96 II E, to remove finish oils. The         test method is described in ASTM Procedure D885, Section 10.                   *The control is an is acetic acid terminated polymer containing 0.06%          TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized with 8        ppm of manganese and 10 ppm of phosphorus.                               

                  TABLE VIII                                                       ______________________________________                                         YARN STABILITY                                                                 YARN BREAKING STRENGTH AFTER HOT/WET                                           TREATMENT 110/30 YARN, ROUND CROSS SECTION                                     Nylon  Conc.      Breaking Strength, Grams                                     Polymer                                                                               & PDMAA    Un-     Treated                                              Number Sample No. treated (1)  5   (2)  %   (3)  %                             ______________________________________                                         Control*          455     337  74  337  74  301  66                            14     10% of # 10                                                                               285     247  86  263  92  237  83                            15     10% of # 11                                                                               297     251  85  259  87  226  76                            21      5% of # 10                                                                               395     357  90  362  92  287  73                            ______________________________________                                          (1) Exposed to boiling water 30 minutes and dried in an air oven 10            minutes at 150° C.                                                      (2) Exposed to boiling water 30 minutes and dried in an air oven 20            minutes at 150° C.                                                      (3) Exposed to boiling water 30 minutes and dried in an air oven 30            minutes at 150° C.                                                

                                      TABLE IX                                     __________________________________________________________________________     LIGHT STABILITY, CARBON ARC                                                                             10 Hours   20 Hours                                   Conc.        Initial            UTS,         UTS,                              Polymer                                                                             and PDMAA                                                                              **UE                                                                               **UTS,                                                                              m/N                                                                               UE UTS,                                                                               m/N **UE                                                                               **UTS,                                                                              m/N                               Number                                                                              Sample Number                                                                          %   gpd  dtex                                                                              %  gpd dtex                                                                               %   gpd  dtex                              __________________________________________________________________________     Control*     26  4.8  42 24 5.1 45  45  25   44                                14   10% of No. 10                                                                          22  3.6  32 20 3.7 33  33  21   31                                15   10% of No. 11                                                                          24  3.5  31 21 3.4 30  30  20   31                                21    5% of No. 11                                                                          24  4.5  40 24 4.8 42  42  23   40                                __________________________________________________________________________      The test method is that described in AATCC Test Model 111C1978 but withou      the humidity control.                                                          *The control is an acetic acid terminated polymer containing 0.06%             TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized with 8        ppm of manganese and 10 ppm of phosphorus.                                     **UE is ultimate elongation, %.                                                UTS is ultimate tensile strength in grams per denier and millinewtons per      decitex.                                                                 

                  TABLE X                                                          ______________________________________                                         CROSS STAINING AND DYED WASHFASTNESS OF                                        YARNS CONTAINING PDMAA BY AATCC TEST 61-1975                                   IIIA (GRAY SCALE)                                                              Nylon                                                                          Polymer Conc. and PDMAA                                                                               Staining       Shade                                    Number  Sample Number  Nylon    Cotton                                                                               Change                                   ______________________________________                                         Control 0              4-5      5     3                                        14      10% of No. 10  4        5     3-4                                      15      10% of No. 11  4        5     3-4                                      21       5% of No. 10  3-4      5     3                                        ______________________________________                                    

All yarns were 110/20 round cross section. They were dyed with 0.,13% Telon fast violet A-BB (Acid Violet 103), and then washed for 45 minutes at 120° F. (49° C.) using the AATCC standard detergent. 

We claim:
 1. The method of preparing a nylon fiber useful for improved comfort for wearers of apparel fabric made therefrom, comprising adding from about 5 to 15% by weight of poly(N,N-dimethylacryamide) having a molecular weight which in a 25% aqueous solution gives a viscosity of from about 20 to 1000 centipoise to from about 85% to 95% by weight caprolactam then polymerizing the mixture conventionally, then extruding and washing the resultant polymer conventionally, then forming the resultant polymer into fiber by conventional spinning.
 2. The method of claim 1 wherein a grafting reaction occurs during polymerization.
 3. The method of claim 2 wherein at least 10% poly(N,N-dimethylacrylamide) is added to the caprolactam.
 4. The method of claim 3 wherein the resultant polymer was formed into fiber by spinning through a spinnerette hole having a length to diameter ratio of from about 4/1 to 8/1. 